The present invention relates to a paper processing device, a paper processing method, and an image forming apparatus which discharge paper sheets upon which predetermined processing has been performed while sorting them into a plurality of positions along a direction which is orthogonal to the direction of paper conveyance.
As is disclosed, for example, in Japanese Laid-Open Patent Publication 2002-154734, in a paper processing device such as an image forming apparatus or the like, it is per se known to provide a sorting mechanism which discharges a plurality of sheets of paper upon which processing has been completed while sorting them into a plurality of positions along a direction which is orthogonal to the direction of paper conveyance. Such a sorting mechanism is termed a shifter mechanism, and it shifts paper ejection rollers which discharge paper in the paper conveyance direction to and fro in the direction orthogonal to the paper conveyance direction, between an initial position and a sorting position. By doing this, the pages of a plurality of copies of a multi-page document upon which processing has been completed are stored in a paper ejection tray, sorted into the individual copies.
As one example, when discharging a page of the (2n−1)th copy (where n=1, 2, 3, . . . ), the sorting mechanism may station the paper ejection rollers in their initial position. And, when discharging a page of the (2n)th copy, after the end portion of the paper sheet has passed the paper ejection rollers which are positioned in their initial position, the sorting mechanism may shift the paper ejection rollers to the sorting position while keeping them in the state in which they are sandwiching the paper sheet between them, and then discharge the paper sheet.
In order to convey a plurality of sheets of paper successively, it is necessary to return the paper ejection rollers which have ejected the page of the (2n)th copy from the sorting position before the leading end of the next sheet of paper arrives at these paper ejection rollers. The plurality of sheets of paper are conveyed successively with a predetermined conveyance gap being provided between the rear end of the first sheet and the leading end of the next sheet. Due to this, the sorting mechanism must return the paper ejection rollers from their sorting position to their initial position during this predetermined conveyance gap.
With image forming apparatus, in recent years, the speed of image formation has been progressively increased. For example there are some such devices which, when conveying a sheet of A4 paper along the direction parallel to its short side, can perform image formation at a paper speed of 600 mm/sec, thus making 100 to 120 copies per minute. With such an image forming apparatus, the paper conveyance gap is about 90 mm, so that, in order to discharge paper one sheet at a time using a sorting mechanism, it is necessary to return the paper ejection rollers from their sorting position to their initial position during a period of 90 mm÷600 mm/sec=0.15 second.
Due to this, with a prior art image forming apparatus which discharges paper one sheet at a time using a sorting mechanism, there has been the problem of a shortage of time for returning the paper ejection rollers from their sorting position to their initial position, so that difficulty has arisen in discharging the pages of a plurality of copies of a document while sorting these pages accurately into different positions for each of the copies. This problem does not only occur with an image forming apparatus; it is a problem which occurs in general with paper processing devices which perform processing at high speed.
A feature of the present invention is to provide an image forming apparatus and, a paper processing method, with which, when paper ejection rollers for performing sorting processing of paper sheets are being shifted to and fro between an initial position and a sorting position, discharges a predetermined number of sheets of paper from the paper ejection rollers in a state in which they are mutually superimposed, so that the time period which can be used for the return movement of the paper ejection rollers is extended, and which can discharge the pages of a plurality of copies of a document while sorting them into the individual copies at high accuracy.